1. Field of the Invention
The present invention relates to presses, and more specifically to pressing tool structures used in press devices for the shaping sheet metal parts, which pressing tools employ elastomeric forming pads for the forming of the sheet metal parts around forming tools.
2. Description of the Prior Art
Press devices for the deformation of sheet metal parts around forming tools and which employ elastomeric forming pads for the application of pressure to the sheet metal parts are known in the art. Such elastomeric forming pads can be used to apply pressure to all sides of the sheet metal parts, and normally these elastomeric forming pads, as well as the sheet metal parts and the forming tools, are located in cavities within the press devices. The pressing force is achieved by placing a "pressing tool" within the cavity of the press device, this pressing tool including an upper tool part, a lower tool part, and the elastomeric forming pad in the forming space therebetween, and then moving the upper tool part down onto the lower tool part which itself is in supporting relationship to the forming tool(s) and the sheet metal part(s) to be shaped. Once the upper tool part has moved downwardly a certain distance, the elastomeric forming pad will completely fill the space in which the forming tool and sheet metal part are positioned, and further movement of the upper tool part will then result in a sharp increase in the pressure within the elastomeric forming pad. Of course, this pressure acts in all directions, generally in the same way as a pressure from within a contained liquid. The forming pad then will press the sheet metal part (work piece) against the forming tool so that the work piece assumes the shape of the forming tool. The great advantages of these types of prior art presses is that the forming pressures can be made very high, e.g. 1000 bar or more, and also that the production capacity can be made very high.
In most cases a rectangular cross-section of the forming space is most practical, both with regard to the utilization of the working space of the press device and with regard to the dimensions of normal work pieces. At the same time, the difficulty and the cost of manufacturing large pressing tools having upper and/or lower parts with a rectangular space for the forming pad increases with the working pressure and the depth of the space. However, a thick forming pad and a large depth in the upper or lower tool part containing the forming pad are required when work pieces with long flanges are to be produced. The stresses at the inner corners of the space will be great and difficult to control due to the bending caused by the outwardly-directed forces from the forming pad. The recesses at the intersection zones between the roof and walls defining the space result in a very unfavorable stress configuration which then necessitates use of undesirable shapes with large recesses and thick walls. All these measures will encroach upon the useful space. The cost of manufacturing forgings increases rapidly with increased size, and the removal of large amounts of material for making room for the forming pad is time-wasting and expensive.
Accordingly, it is an object of the present invention to produce a pressing tool which is constructed to avoid the aforementioned drawbacks.